Fix typo in alert_howto.html (#8964)

public/app/features/alerting/partials/alert_howto.html

@@ -19,7 +19,7 @@
 			Alerts are added and configured in the <strong>Alert Tab</strong> of any dashboard
 			graph panel, letting you build and visualize an alert using existing queries.
 			<br> <br>
-			To persist you alert rule changes remember to save the dashboard.
+			To persist your alert rule changes remember to save the dashboard.
 			<br>
 			<br>
 			<a href="{{appSubUrl}}" class="external-link" ng-click="dismiss()">Go to Home Dashboard</a>